I love Mac OS X's multiple user feature. Although I'm the only person that uses my MacBook Pro, I have three user accounts setup that I use all the time. I have a "Terry White" user (the one I'm in most of the time). I have a "MacGroup" user and I have a "Work" user account (for doing live demonstrations). The beauty of having multiple users is that each user can his/her own preferences, Safari bookmarks, desktop pictures, documents, iTunes libraries, etc. When I'm doing a presentation for MacGroup, I don't want work email notifications popping up. Also i don't want confidential documents showing up by accident in front of an audience. Multiple users has worked well for this for years. The only problem with multiple users comes in when you want to "share" information between those users. No matter how you set permissions to a folder for "all users" to be able to access it, whichever users creates a document and puts it in that folder that user is still the "owner" of that document. This can create issues when other users go to edit and try to save the changes.
Solution: Create a shared Partition
I've been a fan of partitioning my internal hard drive since Mac OS X came out. I create a relatively small partition (80GB on my 500GB drive) and I choose the option when you do a Get Info on that volume to "Ignore ownership on this volume". You can do this for any volume that you're not booting from or have Mac OS X installed on. This means that when I copy files to this volume/partition that I can freely edit those files from any user account without any permission hassles.
The recent versions of Mac OS X also allow you to partition a drive using Disk Utility without having to reformat the whole drive. So I was able to create my most recent partition without losing any data/time. BE SURE TO BACKUP FIRST BEFORE making any changes to your partition sizes! Also depending on the size of the drive and amount of data on it, it can take a while (like a couple of hours) to do the resizing of the partitions because in order to create the new one, it has to also "shrink" the original one.
Did I mention that you should backup first before doing this? I'm not responsible for any loss of your data.